Stereospecific propylene polymers are customarily prepared by contacting propylene monomer with a binary catalyst system. The one component of the catalyst system is a titanium chloride with the second component being an aluminum alkyl. The yield of the polymer obtained per unit of titanium in the catalyst and the ratio of the isotactic polymer to the atactic polymer is importantly influenced by the specific composition of the titanium chloride catalyst and the manner in which it is prepared.
The most productive titanium chloride catalysts and those which give the highest proportions of isotactic to atactic propylene polymer are prepared by preparing the titanium chloride catalyst by treating titanium tetrachloride with an aluminum alkyl compound such as diethyl aluminum chloride (DEAC). It is recognized in the art that the performance of such titanium chloride catalysts can be improved by subsequently treating the titanium chloride catalysts by various methods. One of the treatment methods suggested in the prior art is to heat the titanium chloride catalyst in a hydrocarbon medium with a Lewis base such as dibutyl ether.
Notwithstanding the best techniques reported in the prior art, the productivity of titanium chloride catalysts in terms of grams of propylene polymer produced per gram of titanium is significantly lower than the yield that can be obtained with similar catalysts in the production of ethylene polymers. As a consequence, there is a need in the art for titanium chloride catalysts having a higher productivity for the production of propylene polymers.